The invention relates to a device for blow molding containers which includes a heating section for heating preforms of a thermoplastic material and which is provided with a blow device which includes at least one blow station for deforming the preforms into the containers, wherein a support element for transporting the preforms has at least one positionable clamping element in the area of a head which is insertable into the receiving opening of the preform.
When the deformation of the containers takes place under the influence of blow pressure, preforms of a thermoplastic material, for example, of PET (Polyethylene Terephtalate), are supplied within a blow machine to different processing stations. Typically, such a blow machine has a heating device as well as a blow device in whose areas the previously heated preform is expanded by biaxial orientation into a container. The expansion takes place by means of compressed air which is conducted into the preform to be expanded. The technical sequence of such an expansion of the preform is explained in DE-OS 43 40 291. The introduction of the pressurized gas mentioned above also includes the introduction of compressed gas into the container bladder which is developing in this area as well as the compressed gas introduction into the preform at the beginning of the blow procedure.
The fundamental construction of a blow station for deforming containers is described in DE-OS 42 12 583. Possibilities for addressing the temperature of the preforms are explained in DE-OS-23 52 926.
Within the device for blow moulding, the preforms as well as the expanded containers can be transported by means of different manipulating devices. The use of transport mandrels, which are placed on the preforms, is known in the art. However, the preforms can also be manipulated with other support devices. The use of gripping tongs for manipulating preforms and the use of clamping mandrels, which for support can be inserted into an opening area of the preform, are also among the available constructions.
A manipulation of containers and preforms with the use of transfer wheels is described, for example, in DE-OS 199 06 438 in an arrangement for a transmitting wheel between a blow-wheel and an output section and another transfer wheel between the heating section and the blow-wheel.
The manipulation of the preforms already described above takes place, on the one hand, in accordance with the so called two stage process in which the preforms are initially manufactured in accordance with an injection molding process, are subsequently subjected to intermediate storage and are only later blown up in a container after the temperature thereof has been conditioned. On the other hand, a use in accordance with the so called single process takes place in which the preforms, immediately after being manufactured in accordance with injection molding technology and sufficiently hardened, are adjusted in their temperature and are subsequently blown up.
With respect to blow stations used, different embodiments are known. In blow stations, which are arranged on rotating transport wheels, a book-like turning of the mold carriers is frequently found. However, it is also possible to use other mold carriers which are slidable relative to each other or are guided in some other manner. In stationary blow stations, which are particularly suitable for receiving several cavities for forming the containers, typically plates are used as mold carriers which are arranged parallel to each other.
The transport mandrels used for a transport of the preforms cannot yet meet all requirements which are made with respect to secure transport of the preforms with high transport velocities. In particular, the transport mandrels which are introduced into an opening area of the preforms still have number of deficiencies. The known clamping mandrels are as a rule constructed of a hard core on which is placed on the outer side thereof an O-ring of an Elastomer. When the clamping mandrel, is inserted into the opening area of the preform, the O-ring is elastically deformed and results in a fixing of the preform on the clamping mandrel.
Such a mounting of the preforms has been found unreliable in increasing durations of operation. On the one hand, the inner diameters of the preforms are subject to manufacturing tolerances which lead to different clamping forces. Moreover, the elasticity, and, thus, the resilient force of the elastomer material change with increasing age and in dependence on the respectively prevailing temperature. It is also not possible to apply an excess tension as a precaution on the opening area because such a large tension would lead to deformations of the opening area. Because of these properties of the elastomer materials, it must be expected that a more or less large number of the preforms drop from the clamping mandrels and are not available for a subsequent blowing deformation.
DE 10 2005 011 805 already describes a controllable clamping element which is composed of an elastomer material and is constructed as a spring-like hollow section. As compared to the use of solid sections, for example, in the form of O-rings, it is possible to already achieve significant improvements, however, with respect to the requirements for a uniform and reproducible production of clamping forces for a long operating time, they could still not be met in a satisfactory way.